There are many types of nonwoven webs that have application as particle barrier materials.
Nonwoven webs of very small diameter fibers or microfibers have long been known to be permeable to air and water vapor while remaining relatively impermeable to particles and/or liquid droplets (e.g., aerosols) Useful webs of small diameter fibers can be made by extruding non-elastomeric thermoplastic polymers utilizing fiber forming processes such as, for example, meltblowing processes. Such nonwoven webs of meltblown fibers formed from non-elastomeric polymers are relatively inexpensive and have many applications in limited use or disposable products that are designed to serve a barriers to particulate materials.
Important applications of such materials include, for example, medical and industrial coveralls, filter materials and face masks. In recent years, concern over the filtration efficiency of surgical face masks has grown because of problems associated with acquired immunodeficiency syndrome, tuberculosis and other infectious diseases which may be passed by droplets created in a medical environment as well as the use of laser surgery with its associated aerosol plume created by vaporization of tissue. In many applications of such particle barrier materials, it is desirable to provide a combination of particle barrier properties and porosity Unfortunately, it has been difficult to provide these properties together because conventional methods which increase particle barrier properties generally tend to decrease the porosity of a material.
Thus, a need exists for an inexpensive material which is porous and breathable yet relatively impermeable to particles and/or liquid droplets